A 2-tuple of (resource, remaining-path-segments), or a deferred which
will fire the above.

Causes the object publishing machinery to continue on with specified
resource and segments, calling the appropriate method on the specified
resource.

If you return (self, server.StopTraversal),
this instructs web2 to immediately stop the lookup stage, and switch to the
rendering stage, leaving the remaining path alone for your render function
to handle.